Machines such as dozers, load trucks, motor graders, wheel loaders, etc., are used to perform a variety of tasks at a work site such as moving material and performing other operations. The machines may operate in an autonomous, semi-autonomous, or manual manner to perform these tasks in response to commands generated as part of a work plan for the machines. Autonomously and semi-autonomously operated machines may increase productivity and permit operation in environments that are unsuitable or undesirable for a human operator. Autonomous or semi-autonomous systems may also compensate for inexperienced human operators as well as inefficiencies associated with repetitive tasks.
As a machine performs its tasks, it may receive information and instructions from systems that are located remotely from the machine. In one example, the machine may include a position sensing system having sensors that receive signals from a global navigation satellite system or a global positioning system (collectively referred to as “GPS”). The signals from the GPS may be used to determine the position of the machine. To increase the accuracy of the position sensing system, some machines further include additional systems that work with the GPS. For example, some machines use data from an inertial measurement unit (“IMU”) to supplement the position generated by the GPS. In doing so, the machine may use the IMU data to estimate the position of the machine during the interval between the receipt of GPS signals.
When relying upon GPS signals to establish the position of a machine being operated autonomously or semi-autonomously, early detection of errors in the position sensing system may be desirable. However, certain types of errors in GPS signals such as those caused by multi-path effects, system noise, propagation delays, and other influences may be difficult to detect. This may be particularly true for errors that occur relatively slowly. For example, a newly detected position that would indicate a large change in position may be readily dismissed if a machine is moving relatively slowly. However, determining the accuracy of relatively small changes in position may be more difficult.
U.S. Pat. No. 6,496,778 discloses a positioning system with an inertial measurement unit and a global positioning system processor. The system combines inertial measurement output with global positioning signals to improve the performance of the inertial measurement unit. Output from the inertial measurement unit may subsequently be used in conjunction with the global positioning system to improve the output from the global positioning system.
The foregoing background discussion is intended solely to aid the reader. It is not intended to limit the innovations described herein, nor to limit or expand the prior art discussed. Thus, the foregoing discussion should not be taken to indicate that any particular element of a prior system is unsuitable for use with the innovations described herein, nor is it intended to indicate that any element is essential in implementing the innovations described herein. The implementations and application of the innovations described herein are defined by the appended claims.